Working Families Tax Relief Act of 2019 This bill increases and revises requirements for the refundable earned income and child tax credits. It also makes similar revisions to the earned income tax credit for residents of Puerto Rico. The bill authorizes the Department of the Treasury to regulate the practice of tax return preparers and impose sanctions upon preparers found to be incompetent or disreputable. The Government Accountability Office must study and report on the sharing of information between Treasury and states regarding identification numbers issued to tax return preparers and minimum standards for preparers.